Models and Mechanisms to Explore the Global Oxidation Kinetics of Blends of feed corn stover and Illinois No. 6 Coal

Jillian L Goldfarb

doi:10.4172/2157-7544.1000136

Abstract

Biomass-coal co-firing has the potential to reduce SOx and net CO2 emissions from coal-fired power plants.Given the heterogeneity of biomass and coal feed stocks, the oxidation kinetic behavior of such blends is not wellunderstood. In this investigation, we probe the applicability of a variety of kinetic models to describe the fast oxidationof feed corn stover, Illinois No. 6 coal, and their blends using thermogravimetric analyzer. We find that a first order reaction assumption (often referred to as the Arrhenius Equation), as well as three-dimensional diffusion reaction models offer the best fit to the data as measured through correlation coefficients, and return reasonably similar activation energies. Derivative thermogravimetric curves show that peak mass loss rates occur within ~30K of each other for each fuel and blend, though the peak mass loss rate is dependent on the specific fuel and blend. Evidenceof reaction synergism between the fuels in the blends, in the form of a non-additive activation energy predictionscheme, suggests that the biomass promotes decomposition of the coal at lower temperatures.

Highlights

In 2008 coal accounted for almost 50% of the electricity generated in the United States, while other renewables-defined to include wind, solar and photovoltaic, geothermal, wood and wood-derived fuels, and other biomass-accounted for a mere 3.1% of the total [1]
We investigate the oxidation behavior of feed corn stover (FC), a seasonally available feedstock grown across the U.S, with Illinois No 6 coal (IL), a coal that has been widely studies in the literature
Some studies offer evidence that the kinetics of oxidation of biomass and coal blends are additive in nature, such that each fuel contributes to the activation energy and peak devolatilization rates proportionally to its blend ratio [4]

Summary

Introduction

In 2008 coal accounted for almost 50% of the electricity generated in the United States, while other renewables-defined to include wind, solar and photovoltaic, geothermal, wood and wood-derived fuels, and other biomass-accounted for a mere 3.1% of the total [1]. In addition to probing the behavior of domestically available fuel sources, a second goal of this paper is to determine the applicability of various kinetic expressions to describe the activation energies of oxidation of coalbiomass blends. While extrapolation to large-scale combustion devices is not directly applicable with such data, thermogravimetric analysis is useful from both a fundamental viewpoint in comparison among other samples [4,5,6] These data are useful in modeling combustion for the co-firing of coal-biomass blends, as intrinsic char reactivity is a key factor affecting char burnout in pulverized coal utilization. Our laboratory explores the use of locally sourced, secondgeneration biomass feed stocks as a blended fuel in coal-fired power plants in the Northeast and Mid Atlantic regions.

D2 D3 D4 D5

Results and Discussion

Summary

Conclusions